An FGN reader asked a terrific question about why racers changed skis in the 50k race.

Rosie Brennan, a member of the Dartmouth College XC ski team who spoke with FGN contributor Sarah Odell, offered this explanation:

You do not have to change skis. In fact, it used to be against the rules to
change skis. In many races, it still is. The officials will put a stamp on each
of your skis and you have to finish with at least one of the skis with the
stamps on it (allowing for mishaps and breaking skis). Recently they have
changed the rules and allow for skiers to change skis in the longer races. The
reason you would want to change skis in a longer race is because you might have
missed the wax and either have slow skis or slick skis that make it hard to ski
up the hills. Additionally in long races, kick wax (the sticky stuff just under
the foot that allows you to propel yourself forward) wears off after awhile so
it can be beneficial to switch skis part way through. The reason it was so
prevalant in this Olympics is because the conditions were changing often and
quickly making chosing the right wax very difficult.